1. Field of the Invention
The present invention relates generally to the structure and use of radiofrequency electrosurgical apparatus for the treatment of solid tissue. More particularly, the present invention relates to an electrosurgical system having pairs of electrode arrays which are deployed to treat large volumes of tissue, particularly for the treatment of tumors in the liver and other tissues and organs.
The delivery of radiofrequency energy to treatment regions within solid tissue is known for a variety of purposes. Of particular interest to the present invention, radiofrequency energy may be delivered to diseased regions in target tissue for the purpose of causing tissue necrosis. For example, the liver is a common depository for metastases of many primary cancers, such as cancers of the stomach, bowel, pancreas, kidney, and lung. Electrosurgical probes for deploying multiple electrodes have been designed for the treatment and necrosis of tumors in the liver and other solid tissues. See, for example, the LeVeen™ Needle Electrode available from RadioTherapeutics Corporation which is constructed generally in accord with published PCT application WO 98/52480.
The probes described in WO 98/52480 comprise a number of independent wire electrodes which are extended into tissue from the distal end of a cannula. The wire electrodes may then be energized in a monopolar or bipolar fashion to heat and necrose tissue within a defined generally spherical volumetric region of target tissue. In order to assure that the target tissue is adequately treated and to limit damage to adjacent healthy tissues, it is desirable that the array formed by the wire electrodes within the tissue be precisely and uniformly defined.
Despite the significant success that has accompanied use of the LeVeen™ Needle Electrode in treating solid tissue tumors, the ability to treat particular types of tumors has been somewhat limited. For example, the ability to produce very large tissue lesions, for example lesions having volumes greater than 30–35 cm3, has been problematic. In addition, such larger tumors tend to be less spheroidal in shape than smaller tumors. Since the LeVeen™ Needle Electrode produces generally spheroidal lesions, the ability to treat larger, non-spheroidal tumors can be limited. Additionally, the ability to treat highly vascularized tissues and/or tissue near a large blood vessel has also been limited. In the latter cases, heat being introduced by the electrode can be rapidly carried away by circulating blood, making uniform heating and control of temperature in the vascularized tissues difficult. Uniform heating and temperature control of the tissue being treated is, of course, one prerequisite to obtaining homogenous lesions in and around the tumors.
The ability to provide uniform heating and the creation of homogenous tissue lesions is particularly difficult with bipolar devices. The two bipolar electrodes may be placed in regions with quite different perfusion characteristics, and the heating around each pole can be quite different. That is, one pole may be located adjacent to a large blood vessel, while the other pole may be located adjacent to tissue which is less perfused. Thus, the pole located in the less perfused tissue will heat the tissue immediately surrounding the electrode much more rapidly than the tissue surrounding the opposite polar electrode is heated. In such circumstances, the tissue surrounding one pole may be preferentially heated and necrosed, while the tissue surrounding the other pole will neither be heated nor necrosed sufficiently.
For all these reasons, it would be desirable to provide improved electrosurgical methods and systems for treating tumors in the liver and other body organs. It would be particularly desirable if the methods and systems could produce relatively large lesions (regions of necrosed tissue) within the solid tissue, preferably being capable of producing lesions having volumes greater than 30–35 cm3, more preferably greater than 70 cm3, and even more preferably greater than 150 cm3, or larger. In addition, it would be desirable to provide methods and systems which can uniformly produce tissue lesions in highly vascularized tissues, such as the liver, and even more particularly in tissues which are unevenly perfused, such as tissues which are near major blood vessels, in such organs. It would be still further desirable to provide methods and systems which can produce tissue lesions having a variety of geometries, such as ovoid and cylindrical, rather than just spheroidal. At least some of these objectives will be met by the invention of the present application.
2. Description of the Background Art
U.S. Pat. Nos. 5,827,276; 5,855,576; and 5,868,740 to LeVeen and German Patent Publication No. 2124684 to Stadelmayr describe devices for deploying pairs of axially spaced-apart electrode arrays. U.S. Pat. Nos. 6,090,105; 6,071,280; 5,928,229; 5,913,855; 5,863,290; 5,672,174; and 5,672,173, describe multiple electrode devices having coaxial electrode structures including a primary antenna and at least one curved secondary antenna that deploys from the primary antenna. See, also U.S. Pat. No. 5,611,803 and WO 99/32041.